Hi Sreeram,
I will qualify my answer with i have never used Centos, though I have used a variety of linux distributions including Ubuntu.
From my experience in using robot framework on various distributions is that it doesn't really matter which one you use as the libraries are installed via pip.
Given that there is no licensing cost in installing either, I would suggest taking 2 machines or virtual machines, install both os's (one on each machine) and try them both for a week and then choose whichever one works best for you and your team as both os's are well supported by their respective communities.
Dave.